Stereoscopic motion pictures have been displayed by simultaneously projecting right and left stereo images upon a screen in overlapped relationship while transmitting the light of each image through mutually extinguishing filters, and viewing the overlapped images on the screen through the same mutually extinguishing filters. These filters may comprise colored filters such as red and green, or polarizing filters disposed with their planes of polarization normal to each other.
Prior art devices have used two projectors and two film strips to overlap the projected stereo images upon the screen, one projector having the film for right eye images and the other for left eye images. In the two projector systems, the images were difficult to synchronize, adjustment of the position of the overlapped images was time consuming, the image light intensities were frequently out of balance. Such systems also necessitated the additional expenses of twice as much film as standard motion pictures, extra handling in the projection booth, frequent monitoring, etc. As a result of these technical difficulties and extra costs, the two projector stereoscopic process is no longer used by the motion picture industry.
It has been proposed to print left and right motion picture stereo pictures on a single film frame and to project them simultaneously using a single projector. The stereo pictures may be printed side by side upon the film or one above the other. Mirrors and other optical devices have then been employed to bring the two images into overlapping relationship upon the screen. Such optical devices, however, have had substantial light loss resulting in dull, unsatisfactory projection. Moreover, prior art optical devices employed for stereo projection of single strip stereo images are bulky, difficult to adjust and often require substantial modification for use with the standard motion picture projector.
In this invention the film comprises a pair of stereo pictures with a dark bar centered in a conventional film gate.
Dark bars of equal widths separating images are conventional to films produced by the motion picture industry since the beginning of the century. However, these dark bars are always placed at the rim of the film gate. The dark bar may overlap the edge of the film gate or be hidden entirely, depending on the relative dimensions of the film frame and the gate.
In the present invention two images are placed within a single frame displayed in a single conventional gate, and the dark bar is located at the center of the gate.
The central dark bar and film frame separator strips may be of equal widths, different widths, or in an optimum ratio. The relative positions of the right and left images in the film gate are not easily distinguished. If the correct position of the right and left images in the film gate is reversed then the projected images will appear in pseudo stereo which is objectionable. An alert projectionist can notice the difference after a few seconds and move the film ahead by a half frame thus bringing the images into correct relationship for full stereo. However, it is advantageous to have a means to determine the correct position of the right and left images in the gate.
Accordingly, it is an object of the present invention to provide a stereo conversion system for standard motion picture projectors which will permit the projection of stereoscopic images from a single film strip with little light loss and no modification of the projector.
Another object of the present invention is to provide a stereo conversion system for a motion picture projector which will convert the light coming from each of the projected stereo images on a single frame into polarized beams having their planes of polarization normal to each other and in overlapping relationship upon the screen.
A further object of the present invention is to provide a compact, easily adjusted stereo conversion system for standard motion picture projectors, adaptable to the range of projection lenses of different foci, for the ranges of throw distance and screen sizes usually encountered in motion picture theaters.
Still another object of the present invention is to eliminate the distracting fringe images at the edges of the projection resulting from the two stereo images superimposed upon a screen.
It is another object of this invention to provide a stereo film of maximum image area while eliminating distracting fringe images.
It is another object of this invention to provide indicia or markings to correctly align the right and left images in the film gate while the film is being threaded into projector so that the projected images are always projected in full stereo.